Adding support for networkMode

Adding support for networkMode in startContainerCmd. Default is 'bridge' mode. Also added the test case. 
This adds support for --net option for the docker run command:
--net="bridge"         Set the Network mode for the container
                               'bridge': creates a new network stack for the container on the docker bridge
                               'none': no networking for this container
                               'container:<name|id>': reuses another container network stack
                               'host': use the host network stack inside the container.  Note: the host mode gives the container full access to local system services such as D-bus and is therefore considered insecure.